Process for connecting a shoe sole to its shaft

ABSTRACT

Process and apparatus for connecting the sole of a shoe with its shaft, the sole and the shaft consisting at least partially of thermoplastic synthetic resin, wherein the shaft is placed over a mold corresponding in shape to the shape of the sole, an edge of the shaft protruding over the mold and the shaft being expanded in longitudinal direction of the mold, and wherein subsequently the protruding edge of the shaft is bent over the mold and the sole is pressed against the mold and welded with the bent edge by means of radio frequency.

The present invention refers to a process and an apparatus forconnecting the sole of a shoe with its shaft, noting that said sole andsaid shaft consist at least partially of thermplastic synthetic resin.Shoes of the type described, up till now, have been manufactured byconnecting the sole with the shaft by a seam. This applies particularlyto the inner boots of skiing shoes in which the transition area betweenshaft and sole is not supposed to show a substantially thickenedportion. In this case the sole was bluntly connected to the shaft andskewed with the shaft. Such a procedure suffered from the drawback thatthe seam does not guarantee the required stability for the inner bootwith respect to its shape, that the seam gives an unpleasant appearanceto the shoe and that, in case the inner boot will be worn without theouter boot, the seam will be rapidly worn and will not be water-tight.Therefor, inner boots manufactured in the manner indicated, have beenconnected with the outer boot such, that it became impossible to wearthe inner boot without the outer boot. When manufacturing walking bootsthe shaft usually is pinched over the last and connected, e.g., sewed,with an insole, whereupon a walking sole is applied onto the inner sole.For such an arrangement it is known to provide a shaft, an inner soleand a walking sole of weldable material, and to weld the walking solewith the inner sole and the shaft by means of heating with radiofrequency. However, for such a procedure, it is a prerequisite toconnect and sew, respectively, the shaft with the inner sole.

The present invention now aims at avoiding the drawbacks of knownembodiments of shoes and of processes for producing same, and therefor,the process according to the invention, essentially consists in that theshaft is being put over a mold corresponding in its shape to the shapeof the sole, noting that an edge of the shaft is arranged for protrudingover said mold and that the shaft is being expanded in longitudinaldirection of the mold, and in that subsequently, the protruding edge ofthe shaft is being bent over said mold, and that finally, the sole isbeing pressed in direction to the mold and is being welded with saidbent edge by means of radio frequency.

By welding the sole with the edge protruding over the mold and beingbent over said mold, a firm and permanent connection between the soleand the shaft can be achieved, the strength of said connection beingcapable of coping with any stress condition. Whereas in connecting thebluntly enaging edges of shaft and sole by seams some possibility ofrelative movement between shaft and sole, respectively, must betolerated, in welding these parts a play-free connection is providedthat makes the shoe stable with respect to shape. When the inner bootsfor skiing boots are manufactured in the manner indicated for instance,there is no danger whatsoever to damage the connection between shaft andsole when wearing the inner boot without the outer boot. When bendingthe protruding edge of the shaft over the mold, it might normally bepossible that the material of the shaft becomes ondulated at the area ofstrong curvature of the sole, i.e. at the area of the heel portion andof the toe portion of the sole, which, in turn, might hamper thesubsequent welding operation. However, by elongating or expanding theshaft in longitudinal direction of the mold at the area of its edgesurrounding said mold, the protruding edge of the shaft will be drawnadvantageously in inward direction at the area of strongest curvature,i.e. at the area of the heel portion and of the toe portion, so that theformation of ondulations will be reduced or even avoided at these areas.By welding the parts to be connected by means of radio frequency thesurface portions of the parts to be welded are being heated to maximumtemperature whereas the outer surface of the materials of the sole andof the shaft are not heated to such an extent or even remain cold, sothat an optimal weld is obtained without detracting from appearance andquality of the outer surface.

The invention is of particular advantage for the manufacture of innerboots of skiing boots which have to be put into an outer boot and into ashell, respectively. This manner of manufacturing boots can be appliedto all other types of boots as well, whereby, when a usual insole isomitted, a moccassin type of boot can be produced.

When the materials to be welded are provided with a cover layer, thethickness of materials to be welded may locally differ at the area ofthe welding seam to be produced and this, in view of locally differingpressures applicable, might detract from the quality of the weldobtained. Such an uneven thickness of the materials to be welded, whichmay be present at the area of the protruding edge of the shaft onaccount of ondulations of said shaft or on account of seams, or onaccount of cover layers, according to the invention can be countered byusing a sole having a greater thickness than the thickness of thematerial of the shaft and consisting at least partially of foamedsynthetic plastics material.

When using a sole of a greater thickness than the thickness of the shaftmaterial, any differences in the thickness of the edge of the shaft canbe compensated more easily since the material flows during the weldingoperation. If, in addition, the sole consists of foamed syntheticplastics material, such a compensating effect is getting even morepronounced, because foamed synthetic plastics material can, more orless, be compressed, and if necessary, compressed at the area of thegreatest thickness of the edge of the shaft to such an extent that itspores disappear.

For welding shaft and sole of the shoe it is a prerequisite that bothcomponent parts consist of thermoplastic synthetic material. It willsuffice if only the contacting surfaces of shaft and sole consist ofthermoplastic synthetic material, which implies that the contactingmaterial can easily be provided with a backing layer of other materialthan synthetic thermoplastic material, e.g. a backing layer of leather,textile material or hide.

For the welding by means of radio frequency it is advantageous that theshaft and/or the sole, respectively, consist of polyvinylchloride or, ifdesired, also of polyamides, polyurethanes or polyolefins.

The apparatus for performing the process according to the invention isessentially characterized by a mold having a contour corresponding tothe shape of the sole and by a pair of jaws being movably supported andbeing arranged for being pressed against the mold and for laterallyenclosing the mold, said jaws being provided with rims extending ininward direction overlapping the edge of the mold over its totalcircumference, noting that the rims have a smaller height than the widthof the protruding and bent edge of the shaft, and further characterizedby a press ram cooperating with the mold and having a contourapproximately corresponding to the border line, facing the center of themold, of the rim of the jaws, noting that the mold and the press ram areformed as electrodes being connected to a radio frequency generator. Inview of the rims of the jaws overlapping the edge of the mold over itstotal circumference, the edge of the shaft can be uniformly bent ininward direction. In view of providing a press ram having a contourcorresponding to the bordering line of the rims of the jaws facing thecenter of the mold, this press ram is being applied between said rims,and in view of the mold and the press ram being formed as electrodesbeing connected to a radio frequency generator, the welding is effectedalong a circumference line that is close to the edge of the rims of thejaws.

It is only essential that the height of the rims be smaller than thewidth of the edge of the shaft protruding over the mold so that aportion of said edge of the shaft is maintained accessible for welding.The contour of the mold can be provided with a sharp edge, noting thatthe rims of the jaws enclose an approximately right angle with thosesurfaces of the jaws which are pressed against the mold, so that theprotruding edge of the shaft will be bent at a sharp angle.

The jaws are conveniently arranged for being moved in a plane being inparallel relation to the plane in which, approximately, is located thecontour of the mold corresponding to the shape of the sole. Thus, thejaws are laterally shifted exactly in that direction to the mold inwhich the protruding edge of the shaft is to be bent, so that said edgewill attain the correct bend. In the process according to the inventionit is possible not only to apply plane soles to the edge of the shaft bywelding, but also, to apply soles having a bent shape corresponding tothe shape of the foot as this is the case in boots with heels. In thelatter case the circumference of the mold does not precisely lie in aplane, but in this case it is not only necessary to shift the jaws inparallel relation to that plane in which the circumference of the moldis approximately located. When providing two jaws only, these jaws,according to the invention, can be arranged such, that the partitionline of the jaws, in its position assumed when pressed against the mold,is approximately located in the longitudinal axis of the contour of thesole. This will be sufficient in those cases in which, withoutapplication of heat, the edge of the shaft will be drawn in inwarddirection at the areas of the toe portion and the heel portion byexpanding the shaft in longitudinal direction of the mold, because underthis condition the jaws can engage this edge when being laterallyshifted in direction to the mold. According to the invention, the moldcan be divided into two parts along an oblique plane extending intransverse direction relative to the longitudinal direction of the soleand along an angle relative to the sole deviating from a right angle,noting that both mold parts may be arranged for relative movement. Bythis arrangement, the length of the mold, as seen in longitudinaldirection of the sole, can be reduced by relative shifting movement ofboth mold parts, so that the shaft can be applied to the mold and thenbe expanded or elongated in longitudinal direction of the sole.According to the invention, it is also possible to provide four jaws andto arrange two of them for being shifted in direction of thelongitudinal axis of the circumference of the sole, and to arrange thetwo remaining jaws for being shifted in a direction perpendicular tosaid longitudinal axis.

The invention is further illustrated with reference to the drawingshowing embodiments of the invention in a schematic representation.

FIGS. 1 and 2 show a mold in a side elevation and in a top-plan view,respectively.

FIG. 3 shows a mold together with the shaft applied to the mold.

FIG. 4 shows the jaws in a schematic view.

FIG. 5 shows a section along line V-V of FIG. 3 with the jaws in openedposition.

FIG. 6 shows the mold, the jaws and the press ram prior to welding thesole to the shaft.

FIG. 7 shows the mold, the jaws and the press ram in closed conditionduring welding.

FIG. 8 shows an embodiment comprising four jaws.

1 is the mold being divided into two mold parts 1a and 1b. The mold isdivided along an oblique plane 2. An operating rod 3 is connected to apneumatic cylinder not shown. The mold part 1b can be shifted indirection of the oblique plane 2 in its position 1b', in which the moldis shorter in logitudinal direction of the sole. 4 is the shaft of theshoe, which, as shown in FIG. 3, is applied to the mold 1 such, that theedge 5 of the shaft protrudes in upward direction over the surface 6 ofthe mold. The shaft is being applied to the mold 1 with the mold part 1bassuming its position 1b', i.e. in shortened condition of the mold 1. Inmoving the mold part 1b from its position 1b' into its position 1b, themold is given a greater length so that the edge 5 of the shaft is drawnin inward direction at its front and rear end 5'.

FIG. 4 shows two jaws 7a and 7b of electrically insulating material.These jaws can be shifted in direction of arrows 8 into the positionshown in FIG. 4. Reference numerals 9 indicate pneumatically operatingcylinders.

The jaws 7a and 7b are shown in FIG. 5 together with the mold 1. Thejaws 7a and 7b can be shifted in direction of arrows 8 to assume theposition shown in FIG. 6. The jaws 7a and 7b are provided with a rim 10which serves for bending the edge 5 of the shaft 4 in inward direction.The jaws 7a and 7b are further provided with engaging surfaces 11 whichare pressing the shaft against the side surface of the mold. At thefront and rear ends of the mold, the protruding edge 5 of the shaft isdrawn, as is shown in FIG. 3, in inward direction so that there, therespective edge portion can be easily engaged by the rim 10 of the jaws.As soon as the jaws 7a and 7b assume the position shown in FIG. 6, asole 12 is brought into position for being pressed in downward directionby means of a press ram 13. During this operation, the protruding edge 5is being brought into the position shown in FIG. 7 in which the sole 12is being pressed against the edge 5 of the shaft. The mold 1 and thepress ram 13 consist of metallic material and are connected to theterminals of a radio frequency generator. The mold 1 and the press ram13 thus form electrodes, and by means of the high frequency alternatingfield, the sole 12 is being welded with the edge 5 of the shaft, notingthat the sole 12 and the edge 5 represent a dielectric which is heatedto welding temperature on account of its dielectric losses.

14 is a cover layer applied to the sole for compensating the thicknessof edge 5. 15 is an insert consisting of electrically insulatingmaterial and serving solely for pressing in downward direction thecenter portion of the sole 12 and for limiting the stroke of the pressram 13.

FIG. 4 represents an embodiment comprising two jaws. Of course, it isalso possible to provide, as is shown in FIG. 8, four jaws 7c, 7d, 7eand 7f, which can be moved in direction of arrow 16 into the positionshown in FIG. 8.

What I claim is:
 1. Process for connecting the sole of a shoe with itsshaft, noting that said sole and said shaft consist at least partiallyof thermoplastic synthetic resin, characterized in that the shaft isbeing put over a mold corresponding in its shape to the shape of thesole, noting that an edge of the shaft is allowed to protrude over saidmold and that the shaft is being expanded in longitudinal direction ofthe mold, and in that subsequently the protruding edge of the shaft isbeing bent over said mold and that finally the sole is being pressedagainst the mold and is being welded with said bent edge by means ofradio frequency.
 2. Process as claimed in claim 1, characterized byusing a sole consisting at least partially of foamed synthetic resin andhaving a greater thickness than the material of the shaft.